1. Field of the Invention
This invention relates to an image formation apparatus of a printer, facsimile, copier or the like that uses magnetic toner to form an image, and more particularly to an image formation apparatus, image formation unit and toner mixing unit that is capable of detected the amount of remaining toner.
2. Description of the Related Art
An image formation device forms an electrical latent image on a latent image carrier such as a photosensitive drum, and develops the latent image with toner, then forms a visible image on a sheet by a process of transferring the toner image to a sheet. A developing unit is provided to the printing unit of the image formation apparatus, and a developing roller and a toner-stirring unit are provided to the developing unit.
The developing roller feeds the toner inside the developing unit to the photosensitive drum. The toner stirring unit stirs the toner inside the toner-supply chamber that is connected to the developing chamber, charges the toner, and breaks up any hard toner. This toner is consumed when printing the image. Therefore, when the amount of toner remaining becomes low, it is necessary to supply new toner. In order to automatically detect when the amount of toner is low, there is a toner empty mechanism.
FIGS. 12A to 12F are drawings explaining a conventional toner empty mechanism. A magnetic sensor 100 is located below the developing unit. The magnetic sensor 100 detects the magnetic force of the magnetic toner 120, and generates a detection signal. In part of the stirring element 110 there are stirring blades 112 and a cleaning member 114 made of pliable urethane foam or a rubber blade for wiping toner off of the sensor 100 that detects the residual toner. As this stirring element 110 rotates, the control circuit periodically detects whether or not there is toner in the location of the sensor 100 with the sensor 100, and determines, according to the number of detection times, whether or not to generate a toner empty alarm. FIGS. 12A to 12E shows movements of toner for normal toner flow, and FIG. 12F show the detection waveform of the toner sensor. In FIG. 12F, points (a) to (e) indicate the detection waveform as stirring element 110 rotates. Points (a) to (e) correspond to the stirring element 110 rotary positions depicted in FIG. 12A to FIG. 12E respectively.
As shown in FIG. 12A and FIG. 12B, before the cleaner 114 of the stirring unit 110 passes the position of the sensor 100, the toner normally flows from the rear left to the right, and the waveform of the sensor 100 is high level indicating that there is toner. As shown in FIG. 12C, when the sensor cleaner 114 approaches the position of the sensor 100, the waveform level of the sensor 100 falls. As shown in FIG. 12D and FIG. 12E, after the sensor cleaner 114 has cleaned the position of the sensor 100, toner normally flows from the rear left to the right, and the waveform of the sensor 100 is high level indicating that there is toner.
Moreover, the sensor 100 detects at a fixed cycle whether or not there is toner flowing to the position of the sensor 100, and the control circuit can determine whether or not to generate a toner-empty alarm according to the number of detections.
When the printing operation is performed over a long period of time with little toner consumption, the toner is consumed a very little at a time. Therefore, the toner is stirred for a long time in the printing unit (developing unit), and thereby cutting into an external additive to the toner such as silica for increasing fluidity, the fluidity of the toner extremely worsens.
In that case, the toner with decreased fluidity accumulates in the printing unit in the part other than where the stirring unit 110 is, thereby the cavity of the toner occurs at the sensor position of the stirring unit 110, causing a condition of reduced residual toner in the sensor position. Due to this, the toner sensor 100 detects that the amount of residual toner is low and generates a toner-empty alarm.
FIGS. 13F to 13K are drawings explaining the problems with the related art. The movement of the toner when the fluidity of the toner becomes poor is shown in FIG. 13F to FIG. 13J, and the detection waveform of the toner sensor is shown in FIG. 13K. FIG. 13F and FIG. 13G show the state before the sensor cleaner 114 passes the position of the sensor 100, and FIG. 13H shows the state when the sensor cleaner 114 approaches the position of the sensor 100 and when the level of the waveform drops. As shown in FIG. 13I and FIG. 13J, the sensor cleaner 114 cleans the position of the sensor 100, however, since the fluidity of the toner 120 become poor and the toner 120 does not break up, cavities occur and the toner 120 build up and hardens in the stirring unit 110.
When the fluidity of the toner becomes poor in this way, the toner does not flow smoothly to the sensor position even though there is plenty of toner, and the toner 120 builds up and hardens in the stirring unit 110 and the sensor 100 is not able to detect the toner and thus generates a toner-empty alarm.
When a toner-empty alarm is generated, the user must fill the toner according to the manual regardless of whether there is toner in the printing unit. However, in that case, since more toner than is necessary is filled inside the printing unit, the build up of toner further increases, and the hollow cavities increase, thus a toner-empty alarm is mistakenly detected again.
When used under the above conditions, abnormal pressure occurs inside the printing unit, trouble such as blown toner or toner leakage occurs, causing problems in printing.
An objective of this invention is to provide an image formation apparatus, image formation unit and toner stirring unit for accurately detecting when toner is empty even when fluidity of the magnetic toner decreases.
Another objective of this invention is to provide an image formation apparatus, image formation unit and toner stirring unit in which a sensor accurately detects whether or not there is not even when fluidity of the magnetic toner decreases.
In order to accomplish these objectives, the image formation apparatus and image formation unit of this invention comprises: a developing unit for developing a latent image on the latent image carrier with magnetic toner; and a toner sensor for detecting whether or not there is magnetic toner in the developer. The developing unit comprises: cleaning member for cleaning the position of the toner sensor, and a stirring unit having a toner accumulation part and a magnetic metal member.
In this invention, the magnetic metal member for preventing erroneous detection of the toner empty alarm, and toner accumulation part are provided at the position of the sensor of the stirring unit, so the toner sensor can generate output of detecting the toner even when the fluidity of the magnetic toner is poor, thus it is possible to prevent erroneous toner empty detection. Therefore, there is no erroneous detection of the toner empty alarm, making it possible to prevent toner from being over supplied, as well as prevent toner from being blown out or leaking, and thus normal printing is possible. Also, since the residual toner is properly managed, it is possible to consume toner without wasting any.
Moreover, in this invention, the apparatus or the unit further have a control circuit for detecting when the toner is empty from the output of the toner sensor after one turn of the stirring unit. Therefore, it is possible to accurately detect when the toner is empty even when there is a cleaning unit.
Furthermore, in this invention, the toner accumulation part is located in one area around the rotating shaft of the stirring unit, and the magnetic metal member is provided to another area around the rotating shaft of the stirring unit. Therefore, it is possible for the toner sensor to more accurately generate output of the synthetically detected toner.